In recent years, so-called network cameras are installed, which are controlled by remote operation via a network or a dedicated line and capture images for the purpose of grasping the situation of roads or rivers, preventing crimes, and the like. In such a camera, improvement of image quality for photographing clearer images, and increase of magnification, that is, increase of zooming for photographing farther, are progressing. There are also a fixed type camera for photographing only in one direction, and a turning type camera capable of panning that is rotation in the horizontal direction or tilting that is rotation in the vertical direction.
The turning type camera often has a preset function. The preset function is a function for automatically turning the camera to a pre-registered preset position and performing photographing. In such a function, to accurately stop the camera at the registered position, high stop position accuracy is required of a mechanism for turning the camera. In addition, in a camera having a zoom function, since the ratio of the turning angle to the angle of view is relatively large, the importance of the stop position accuracy is high.
The stop position accuracy of the mechanism for turning the camera will be described with reference to a pan turning mechanism illustrated in FIGS. 29 to 34. This pan turning mechanism includes a worm 33 to which a pan motor 32 is attached, and a worm wheel 34 to which a camera 10 is attached.
FIG. 30 is a diagram of the pan turning mechanism of FIG. 29 as viewed from a direction A in the figure. The teeth of the worm 33 engage with the teeth of the worm wheel 34, and the pan motor 32 rotates in the forward rotational direction or the reverse rotational direction, whereby the camera 10 is turned to a desired position.
FIG. 31 is a diagram illustrating the engagement between the teeth of the worm 33 and the teeth of the worm wheel 34. In the pan turning mechanism transmitting the rotational force by tooth engagement, to prevent a load from being increased by interference between the teeth due to the distance between the shafts, manufacturing errors, and the like, a backlash, that is, a gap between the gears is necessary. In this figure, a total number of teeth of the worm wheel 34 is 120, and a tooth angle 34a is 3 degrees. In addition, the backlash, that is, a gap 33a+a gap 33b is 0.03 degrees. Each angle of the tooth angle 34a, and the gaps 33a and 33b indicates an angle as viewed from the rotation center of the worm wheel 34.
FIG. 32 is a diagram illustrating engagement when the worm 33 is rotated forward. The teeth of the worm 33 and the teeth of the worm wheel 34 come into contact with each other on the gap 33a side, whereby the worm wheel 34 rotates in the forward rotational direction.
FIG. 33 is a diagram illustrating engagement when the worm 33 is rotated reversely. In contrast with the forward rotation, in the reverse rotation, the teeth of the worm 33 and the teeth of the worm wheel 34 come in contact with each other on the opposite gap 33b side, whereby the worm wheel 34 rotates in the reverse rotational direction.
With reference to FIG. 34, a phenomenon will be described in which a stop position error occurs in a mechanism transmitting rotational force by such tooth engagement. When the worm wheel 34 is rotated by 270 degrees in the forward rotational direction from a current position and then the worm wheel 34 is rotated by 270 degrees in the reverse rotational direction from that position, the worm wheel returns to the same position fundamentally. However, in the case of a configuration in which the worm wheel 34 is rotated by rotating the worm 33, when the worm 33 is rotated in the forward rotational direction from the engagement state illustrated in FIG. 32 and then rotated in the reverse rotational direction, the worm wheel 34 fails to rotate by degrees corresponding to a space of the gap 33a+the gap 33b. An angular error occurs in the worm wheel 34 by the space, and thus when the rotational operation of 270 degrees is completed in the reverse rotational direction, a stop position error occurs by the space of the gap 33a+the gap 33b in the forward rotational direction from the initial current position. In this illustrated example, the stop position error is 0.03 degrees. Note that, the stop position error due to the backlash as described above occurs not only in panning but also in tilting.
In view of the occurrence of such a stop position error, for example, Patent Literature 1 discloses an image pickup device for preparing a stop position correction value table in which a stop position error amount that is calculated or measured in advance is set, and adjusting a cutout position in a photographed image by using the table. As a result, an image in which the stop position error is reduced can be used as a display image.